1. Technical Field
The present invention relates to a droplet ejecting apparatus.
2. Related Art
In a serial ink jet printer, dots are formed on a plurality of raster lines which are aligning in the sub-scanning direction by repeating a main scanning pass which forms the dots by ejecting ink from nozzles of a print head, and sub-scanning in which a medium is moved relative to the sub-scanning direction which intersects the main scanning direction while relatively moving the print head and the medium in the main scanning direction, and an image is printed on the medium. In addition, as a method of forming dots on the raster line, there is a single pass method in which forming of dots on a raster line is completed using one main scanning pass, and a multipass method in which forming of dots on the raster line is completed using main scanning passes of N times (N is integer of 2 or greater).
In the ink jet printer, there is a case in which ink is not ejected due to clogging of nozzles which is caused by thickening of ink, mixing of bubbles, or the like. When nozzles are clogged, dot omission occurs in an image, and deterioration of image quality is caused. Therefore, there is a case in which nozzle checking, cleaning of head (wiping, suction of ink, flushing, or the like) is performed in an ink jet printer in the related art, in order to suppress deterioration in image quality of an image which is caused by defective ejecting of ink from nozzles. For example, in JP-A-2010-30184, a technology is disclosed in which defective printing caused by an occurrence of a nozzle of which ejecting of ink is defective (hereinafter, referred to as “defective nozzle”) is suppressed by executing a nozzle inspection even in the middle of printing, when the number of counting passes (corresponding to number of main scanning passes) in continuous printing exceeds a threshold value in the continuous printing in which printing is continuously performed with respect to a plurality of labels. At this time, as the threshold value of the number of counting passes, a small value is used in a printing mode of which a set reliability is high, and in contrast to this, a large value is used in a printing mode of which a set reliability is low. Accordingly, nozzle inspection timing is changed according to a set reliability of printing. In addition, hereinafter, as in the nozzle inspection, or head cleaning, a process of checking an ejecting state of a head, or a process of recovering the ejecting state of the head will be also referred to as a “maintenance process”.
Here, in the ink jet printer, in order to suppress the above described deterioration in image quality of an image due to defective printing which is caused by defective nozzles, it is desirable to execute a maintenance process as much as possible even in the middle of printing. However, there is the following problem when executing a maintenance process in the middle of printing.
When executing a maintenance process in the middle of printing with respect to one medium, there is a possibility that a difference may occur in a forming state between a dot formed in a main scanning pass which is performed immediately before the maintenance process and a dot formed in a main scanning pass which is performed immediately after the maintenance process due to a stop time which is caused by the maintenance process, and deterioration in image quality due to color unevenness caused by the difference becomes obvious. For example, since a dot in the main scanning pass performed immediately before the maintenance process and a dot in the main scanning pass performed immediately after the maintenance process are mixed in a plurality of dots which are aligned on one raster line in the multipass method, there is a possibility that color unevenness due to mixing of dots may become obvious.
In addition, the above described problem is not a problem limited to a serial ink jet printer, and is a common problem in a droplet ejecting apparatus which records dots by ejecting droplets on a medium.